/* pngwutil.c - utilities to write a PNG file
 *
 * Last changed in libpng 1.4.1 [February 25, 2010]
 * Copyright (c) 1998-2010 Glenn Randers-Pehrson
 * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
 * (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
 *
 * This code is released under the libpng license.
 * For conditions of distribution and use, see the disclaimer
 * and license in png.h
 */

#include "png.h"
#define PNG_NO_PEDANTIC_WARNINGS
#ifdef PNG_WRITE_SUPPORTED
    #include "pngpriv.h"

/* Place a 32-bit number into a buffer in PNG byte order.  We work
 * with unsigned numbers for convenience, although one supported
 * ancillary chunk uses signed (two's complement) numbers.
 */
void PNGAPI
png_save_uint_32(png_bytep buf, png_uint_32 i)
{
    buf[0] = (png_byte)((i >> 24) & 0xff);
    buf[1] = (png_byte)((i >> 16) & 0xff);
    buf[2] = (png_byte)((i >> 8) & 0xff);
    buf[3] = (png_byte)(i & 0xff);
}

    #ifdef PNG_SAVE_INT_32_SUPPORTED
/* The png_save_int_32 function assumes integers are stored in two's
 * complement format.  If this isn't the case, then this routine needs to
 * be modified to write data in two's complement format.
 */
void PNGAPI
png_save_int_32(png_bytep buf, png_int_32 i)
{
    buf[0] = (png_byte)((i >> 24) & 0xff);
    buf[1] = (png_byte)((i >> 16) & 0xff);
    buf[2] = (png_byte)((i >> 8) & 0xff);
    buf[3] = (png_byte)(i & 0xff);
}
    #endif

/* Place a 16-bit number into a buffer in PNG byte order.
 * The parameter is declared unsigned int, not png_uint_16,
 * just to avoid potential problems on pre-ANSI C compilers.
 */
void PNGAPI
png_save_uint_16(png_bytep buf, unsigned int i)
{
    buf[0] = (png_byte)((i >> 8) & 0xff);
    buf[1] = (png_byte)(i & 0xff);
}

/* Simple function to write the signature.  If we have already written
 * the magic bytes of the signature, or more likely, the PNG stream is
 * being embedded into another stream and doesn't need its own signature,
 * we should call png_set_sig_bytes() to tell libpng how many of the
 * bytes have already been written.
 */
void PNGAPI
png_write_sig(png_structp png_ptr)
{
    png_byte png_signature[8] = { 137, 80, 78, 71, 13, 10, 26, 10 };

    #ifdef PNG_IO_STATE_SUPPORTED
    /* Inform the I/O callback that the signature is being written */
    png_ptr->io_state = PNG_IO_WRITING | PNG_IO_SIGNATURE;
    #endif

    /* Write the rest of the 8 byte signature */
    png_write_data(png_ptr, &png_signature[png_ptr->sig_bytes],
                   (png_size_t)(8 - png_ptr->sig_bytes));
    if (png_ptr->sig_bytes < 3)
        png_ptr->mode |= PNG_HAVE_PNG_SIGNATURE;
}

/* Write a PNG chunk all at once.  The type is an array of ASCII characters
 * representing the chunk name.  The array must be at least 4 bytes in
 * length, and does not need to be null terminated.  To be safe, pass the
 * pre-defined chunk names here, and if you need a new one, define it
 * where the others are defined.  The length is the length of the data.
 * All the data must be present.  If that is not possible, use the
 * png_write_chunk_start(), png_write_chunk_data(), and png_write_chunk_end()
 * functions instead.
 */
void PNGAPI
png_write_chunk(png_structp png_ptr, png_bytep chunk_name,
                png_bytep data, png_size_t length)
{
    if (png_ptr == NULL)
        return;
    png_write_chunk_start(png_ptr, chunk_name, (png_uint_32)length);
    png_write_chunk_data(png_ptr, data, (png_size_t)length);
    png_write_chunk_end(png_ptr);
}

/* Write the start of a PNG chunk.  The type is the chunk type.
 * The total_length is the sum of the lengths of all the data you will be
 * passing in png_write_chunk_data().
 */
void PNGAPI
png_write_chunk_start(png_structp png_ptr, png_bytep chunk_name,
                      png_uint_32 length)
{
    png_byte buf[8];

    png_debug2(0, "Writing %s chunk, length = %lu", chunk_name,
               (unsigned long)length);

    if (png_ptr == NULL)
        return;

    #ifdef PNG_IO_STATE_SUPPORTED
    /* Inform the I/O callback that the chunk header is being written.
     * PNG_IO_CHUNK_HDR requires a single I/O call.
     */
    png_ptr->io_state = PNG_IO_WRITING | PNG_IO_CHUNK_HDR;
    #endif

    /* Write the length and the chunk name */
    png_save_uint_32(buf, length);
    png_memcpy(buf + 4, chunk_name, 4);
    png_write_data(png_ptr, buf, (png_size_t)8);
    /* Put the chunk name into png_ptr->chunk_name */
    png_memcpy(png_ptr->chunk_name, chunk_name, 4);
    /* Reset the crc and run it over the chunk name */
    png_reset_crc(png_ptr);
    png_calculate_crc(png_ptr, chunk_name, 4);

    #ifdef PNG_IO_STATE_SUPPORTED
    /* Inform the I/O callback that chunk data will (possibly) be written.
     * PNG_IO_CHUNK_DATA does NOT require a specific number of I/O calls.
     */
    png_ptr->io_state = PNG_IO_WRITING | PNG_IO_CHUNK_DATA;
    #endif
}

/* Write the data of a PNG chunk started with png_write_chunk_start().
 * Note that multiple calls to this function are allowed, and that the
 * sum of the lengths from these calls *must* add up to the total_length
 * given to png_write_chunk_start().
 */
void PNGAPI
png_write_chunk_data(png_structp png_ptr, png_bytep data, png_size_t length)
{
    /* Write the data, and run the CRC over it */
    if (png_ptr == NULL)
        return;
    if (data != NULL && length > 0)
    {
        png_write_data(png_ptr, data, length);
        /* Update the CRC after writing the data,
         * in case that the user I/O routine alters it.
         */
        png_calculate_crc(png_ptr, data, length);
    }
}

/* Finish a chunk started with png_write_chunk_start(). */
void PNGAPI
png_write_chunk_end(png_structp png_ptr)
{
    png_byte buf[4];

    if (png_ptr == NULL) return;

    #ifdef PNG_IO_STATE_SUPPORTED
    /* Inform the I/O callback that the chunk CRC is being written.
     * PNG_IO_CHUNK_CRC requires a single I/O function call.
     */
    png_ptr->io_state = PNG_IO_WRITING | PNG_IO_CHUNK_CRC;
    #endif

    /* Write the crc in a single operation */
    png_save_uint_32(buf, png_ptr->crc);

    png_write_data(png_ptr, buf, (png_size_t)4);
}

    #if defined (PNG_WRITE_TEXT_SUPPORTED) || defined (PNG_WRITE_iCCP_SUPPORTED)
/* This pair of functions encapsulates the operation of (a) compressing a
 * text string, and (b) issuing it later as a series of chunk data writes.
 * The compression_state structure is shared context for these functions
 * set up by the caller in order to make the whole mess thread-safe.
 */

typedef struct
{
    char* input;  /* The uncompressed input data */
    int input_len;  /* Its length */
    int num_output_ptr; /* Number of output pointers used */
    int max_output_ptr; /* Size of output_ptr */
    png_charpp output_ptr; /* Array of pointers to output */
} compression_state;

/* Compress given text into storage in the png_ptr structure */
static int /* PRIVATE */
png_text_compress(png_structp png_ptr,
                  png_charp text, png_size_t text_len, int compression,
                  compression_state* comp)
{
    int ret;

    comp->num_output_ptr = 0;
    comp->max_output_ptr = 0;
    comp->output_ptr = NULL;
    comp->input = NULL;
    comp->input_len = 0;

    /* We may just want to pass the text right through */
    if (compression == PNG_TEXT_COMPRESSION_NONE)
    {
        comp->input = text;
        comp->input_len = text_len;
        return ((int)text_len);
    }

    if (compression >= PNG_TEXT_COMPRESSION_LAST)
    {
        #ifdef PNG_STDIO_SUPPORTED
        char msg[50];
        png_snprintf(msg, 50, "Unknown compression type %d", compression);
        png_warning(png_ptr, msg);
        #else
        png_warning(png_ptr, "Unknown compression type");
        #endif
    }

    /* We can't write the chunk until we find out how much data we have,
     * which means we need to run the compressor first and save the
     * output.  This shouldn't be a problem, as the vast majority of
     * comments should be reasonable, but we will set up an array of
     * malloc'd pointers to be sure.
     *
     * If we knew the application was well behaved, we could simplify this
     * greatly by assuming we can always malloc an output buffer large
     * enough to hold the compressed text ((1001 * text_len / 1000) + 12)
     * and malloc this directly.  The only time this would be a bad idea is
     * if we can't malloc more than 64K and we have 64K of random input
     * data, or if the input string is incredibly large (although this
     * wouldn't cause a failure, just a slowdown due to swapping).
     */

    /* Set up the compression buffers */
    png_ptr->zstream.avail_in = (uInt)text_len;
    png_ptr->zstream.next_in = (Bytef*)text;
    png_ptr->zstream.avail_out = (uInt)png_ptr->zbuf_size;
    png_ptr->zstream.next_out = (Bytef*)png_ptr->zbuf;

    /* This is the same compression loop as in png_write_row() */
    do
    {
        /* Compress the data */
        ret = deflate(&png_ptr->zstream, Z_NO_FLUSH);
        if (ret != Z_OK)
        {
            /* Error */
            if (png_ptr->zstream.msg != NULL)
                png_error(png_ptr, png_ptr->zstream.msg);
            else
                png_error(png_ptr, "zlib error");
        }
        /* Check to see if we need more room */
        if (!(png_ptr->zstream.avail_out))
        {
            /* Make sure the output array has room */
            if (comp->num_output_ptr >= comp->max_output_ptr)
            {
                int old_max;

                old_max = comp->max_output_ptr;
                comp->max_output_ptr = comp->num_output_ptr + 4;
                if (comp->output_ptr != NULL)
                {
                    png_charpp old_ptr;

                    old_ptr = comp->output_ptr;
                    comp->output_ptr = (png_charpp)png_malloc(png_ptr,
                                                              (png_alloc_size_t)
                                                              (comp->max_output_ptr * png_sizeof(png_charpp)));
                    png_memcpy(comp->output_ptr, old_ptr, old_max
                               * png_sizeof(png_charp));
                    png_free(png_ptr, old_ptr);
                }
                else
                    comp->output_ptr = (png_charpp)png_malloc(png_ptr,
                                                              (png_alloc_size_t)
                                                              (comp->max_output_ptr * png_sizeof(png_charp)));
            }

            /* Save the data */
            comp->output_ptr[comp->num_output_ptr] =
                (png_charp)png_malloc(png_ptr,
                                      (png_alloc_size_t)png_ptr->zbuf_size);
            png_memcpy(comp->output_ptr[comp->num_output_ptr], png_ptr->zbuf,
                       png_ptr->zbuf_size);
            comp->num_output_ptr++;

            /* and reset the buffer */
            png_ptr->zstream.avail_out = (uInt)png_ptr->zbuf_size;
            png_ptr->zstream.next_out = png_ptr->zbuf;
        }
        /* Continue until we don't have any more to compress */
    }
    while (png_ptr->zstream.avail_in);

    /* Finish the compression */
    do
    {
        /* Tell zlib we are finished */
        ret = deflate(&png_ptr->zstream, Z_FINISH);

        if (ret == Z_OK)
        {
            /* Check to see if we need more room */
            if (!(png_ptr->zstream.avail_out))
            {
                /* Check to make sure our output array has room */
                if (comp->num_output_ptr >= comp->max_output_ptr)
                {
                    int old_max;

                    old_max = comp->max_output_ptr;
                    comp->max_output_ptr = comp->num_output_ptr + 4;
                    if (comp->output_ptr != NULL)
                    {
                        png_charpp old_ptr;

                        old_ptr = comp->output_ptr;
                        /* This could be optimized to realloc() */
                        comp->output_ptr = (png_charpp)png_malloc(png_ptr,
                                                                  (png_alloc_size_t)(comp->max_output_ptr *
                                                                                     png_sizeof(png_charp)));
                        png_memcpy(comp->output_ptr, old_ptr,
                                   old_max * png_sizeof(png_charp));
                        png_free(png_ptr, old_ptr);
                    }
                    else
                        comp->output_ptr = (png_charpp)png_malloc(png_ptr,
                                                                  (png_alloc_size_t)(comp->max_output_ptr *
                                                                                     png_sizeof(png_charp)));
                }

                /* Save the data */
                comp->output_ptr[comp->num_output_ptr] =
                    (png_charp)png_malloc(png_ptr,
                                          (png_alloc_size_t)png_ptr->zbuf_size);
                png_memcpy(comp->output_ptr[comp->num_output_ptr], png_ptr->zbuf,
                           png_ptr->zbuf_size);
                comp->num_output_ptr++;

                /* and reset the buffer pointers */
                png_ptr->zstream.avail_out = (uInt)png_ptr->zbuf_size;
                png_ptr->zstream.next_out = png_ptr->zbuf;
            }
        }
        else if (ret != Z_STREAM_END)
        {
            /* We got an error */
            if (png_ptr->zstream.msg != NULL)
                png_error(png_ptr, png_ptr->zstream.msg);
            else
                png_error(png_ptr, "zlib error");
        }
    }
    while (ret != Z_STREAM_END);

    /* Text length is number of buffers plus last buffer */
    text_len = png_ptr->zbuf_size * comp->num_output_ptr;
    if (png_ptr->zstream.avail_out < png_ptr->zbuf_size)
        text_len += png_ptr->zbuf_size - (png_size_t)png_ptr->zstream.avail_out;

    return ((int)text_len);
}

/* Ship the compressed text out via chunk writes */
static void /* PRIVATE */
png_write_compressed_data_out(png_structp png_ptr, compression_state* comp)
{
    int i;

    /* Handle the no-compression case */
    if (comp->input)
    {
        png_write_chunk_data(png_ptr, (png_bytep)comp->input,
                             (png_size_t)comp->input_len);
        return;
    }

    /* Write saved output buffers, if any */
    for (i = 0; i < comp->num_output_ptr; i++)
    {
        png_write_chunk_data(png_ptr, (png_bytep)comp->output_ptr[i],
                             (png_size_t)png_ptr->zbuf_size);
        png_free(png_ptr, comp->output_ptr[i]);
    }
    if (comp->max_output_ptr != 0)
        png_free(png_ptr, comp->output_ptr);
    /* Write anything left in zbuf */
    if (png_ptr->zstream.avail_out < (png_uint_32)png_ptr->zbuf_size)
        png_write_chunk_data(png_ptr, png_ptr->zbuf,
                             (png_size_t)(png_ptr->zbuf_size - png_ptr->zstream.avail_out));

    /* Reset zlib for another zTXt/iTXt or image data */
    deflateReset(&png_ptr->zstream);
    png_ptr->zstream.data_type = Z_BINARY;
}
    #endif

/* Write the IHDR chunk, and update the png_struct with the necessary
 * information.  Note that the rest of this code depends upon this
 * information being correct.
 */
void /* PRIVATE */
png_write_IHDR(png_structp png_ptr, png_uint_32 width, png_uint_32 height,
               int bit_depth, int color_type, int compression_type, int filter_type,
               int interlace_type)
{
    PNG_IHDR;
    int ret;

    png_byte buf[13]; /* Buffer to store the IHDR info */

    png_debug(1, "in png_write_IHDR");

    /* Check that we have valid input data from the application info */
    switch (color_type)
    {
        case PNG_COLOR_TYPE_GRAY:
            switch (bit_depth)
            {
                case 1:
                case 2:
                case 4:
                case 8:
                case 16: png_ptr->channels = 1; break;
                default: png_error(png_ptr,
                                   "Invalid bit depth for grayscale image");
            }
            break;
        case PNG_COLOR_TYPE_RGB:
            if (bit_depth != 8 && bit_depth != 16)
                png_error(png_ptr, "Invalid bit depth for RGB image");
            png_ptr->channels = 3;
            break;
        case PNG_COLOR_TYPE_PALETTE:
            switch (bit_depth)
            {
                case 1:
                case 2:
                case 4:
                case 8: png_ptr->channels = 1; break;
                default: png_error(png_ptr, "Invalid bit depth for paletted image");
            }
            break;
        case PNG_COLOR_TYPE_GRAY_ALPHA:
            if (bit_depth != 8 && bit_depth != 16)
                png_error(png_ptr, "Invalid bit depth for grayscale+alpha image");
            png_ptr->channels = 2;
            break;
        case PNG_COLOR_TYPE_RGB_ALPHA:
            if (bit_depth != 8 && bit_depth != 16)
                png_error(png_ptr, "Invalid bit depth for RGBA image");
            png_ptr->channels = 4;
            break;
        default:
            png_error(png_ptr, "Invalid image color type specified");
    }

    if (compression_type != PNG_COMPRESSION_TYPE_BASE)
    {
        png_warning(png_ptr, "Invalid compression type specified");
        compression_type = PNG_COMPRESSION_TYPE_BASE;
    }

    /* Write filter_method 64 (intrapixel differencing) only if
     * 1. Libpng was compiled with PNG_MNG_FEATURES_SUPPORTED and
     * 2. Libpng did not write a PNG signature (this filter_method is only
     *    used in PNG datastreams that are embedded in MNG datastreams) and
     * 3. The application called png_permit_mng_features with a mask that
     *    included PNG_FLAG_MNG_FILTER_64 and
     * 4. The filter_method is 64 and
     * 5. The color_type is RGB or RGBA
     */
    if (
        #ifdef PNG_MNG_FEATURES_SUPPORTED
        !((png_ptr->mng_features_permitted & PNG_FLAG_MNG_FILTER_64) &&
          ((png_ptr->mode & PNG_HAVE_PNG_SIGNATURE) == 0) &&
          (color_type == PNG_COLOR_TYPE_RGB ||
           color_type == PNG_COLOR_TYPE_RGB_ALPHA) &&
          (filter_type == PNG_INTRAPIXEL_DIFFERENCING)) &&
        #endif
        filter_type != PNG_FILTER_TYPE_BASE)
    {
        png_warning(png_ptr, "Invalid filter type specified");
        filter_type = PNG_FILTER_TYPE_BASE;
    }

    #ifdef PNG_WRITE_INTERLACING_SUPPORTED
    if (interlace_type != PNG_INTERLACE_NONE &&
        interlace_type != PNG_INTERLACE_ADAM7)
    {
        png_warning(png_ptr, "Invalid interlace type specified");
        interlace_type = PNG_INTERLACE_ADAM7;
    }
    #else
    interlace_type = PNG_INTERLACE_NONE;
    #endif

    /* Save the relevent information */
    png_ptr->bit_depth = (png_byte)bit_depth;
    png_ptr->color_type = (png_byte)color_type;
    png_ptr->interlaced = (png_byte)interlace_type;
    #ifdef PNG_MNG_FEATURES_SUPPORTED
    png_ptr->filter_type = (png_byte)filter_type;
    #endif
    png_ptr->compression_type = (png_byte)compression_type;
    png_ptr->width = width;
    png_ptr->height = height;

    png_ptr->pixel_depth = (png_byte)(bit_depth * png_ptr->channels);
    png_ptr->rowbytes = PNG_ROWBYTES(png_ptr->pixel_depth, width);
    /* Set the usr info, so any transformations can modify it */
    png_ptr->usr_width = png_ptr->width;
    png_ptr->usr_bit_depth = png_ptr->bit_depth;
    png_ptr->usr_channels = png_ptr->channels;

    /* Pack the header information into the buffer */
    png_save_uint_32(buf, width);
    png_save_uint_32(buf + 4, height);
    buf[8] = (png_byte)bit_depth;
    buf[9] = (png_byte)color_type;
    buf[10] = (png_byte)compression_type;
    buf[11] = (png_byte)filter_type;
    buf[12] = (png_byte)interlace_type;

    /* Write the chunk */
    png_write_chunk(png_ptr, (png_bytep)png_IHDR, buf, (png_size_t)13);

    /* Initialize zlib with PNG info */
    png_ptr->zstream.zalloc = png_zalloc;
    png_ptr->zstream.zfree = png_zfree;
    png_ptr->zstream.opaque = (voidpf)png_ptr;
    if (!(png_ptr->do_filter))
    {
        if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE ||
            png_ptr->bit_depth < 8)
            png_ptr->do_filter = PNG_FILTER_NONE;
        else
            png_ptr->do_filter = PNG_ALL_FILTERS;
    }
    if (!(png_ptr->flags & PNG_FLAG_ZLIB_CUSTOM_STRATEGY))
    {
        if (png_ptr->do_filter != PNG_FILTER_NONE)
            png_ptr->zlib_strategy = Z_FILTERED;
        else
            png_ptr->zlib_strategy = Z_DEFAULT_STRATEGY;
    }
    if (!(png_ptr->flags & PNG_FLAG_ZLIB_CUSTOM_LEVEL))
        png_ptr->zlib_level = Z_DEFAULT_COMPRESSION;
    if (!(png_ptr->flags & PNG_FLAG_ZLIB_CUSTOM_MEM_LEVEL))
        png_ptr->zlib_mem_level = 8;
    if (!(png_ptr->flags & PNG_FLAG_ZLIB_CUSTOM_WINDOW_BITS))
        png_ptr->zlib_window_bits = 15;
    if (!(png_ptr->flags & PNG_FLAG_ZLIB_CUSTOM_METHOD))
        png_ptr->zlib_method = 8;
    ret = deflateInit2(&png_ptr->zstream, png_ptr->zlib_level,
                       png_ptr->zlib_method, png_ptr->zlib_window_bits,
                       png_ptr->zlib_mem_level, png_ptr->zlib_strategy);
    if (ret != Z_OK)
    {
        if (ret == Z_VERSION_ERROR) png_error(png_ptr,
                                              "zlib failed to initialize compressor -- version error");
        if (ret == Z_STREAM_ERROR) png_error(png_ptr,
                                             "zlib failed to initialize compressor -- stream error");
        if (ret == Z_MEM_ERROR) png_error(png_ptr,
                                          "zlib failed to initialize compressor -- mem error");
        png_error(png_ptr, "zlib failed to initialize compressor");
    }
    png_ptr->zstream.next_out = png_ptr->zbuf;
    png_ptr->zstream.avail_out = (uInt)png_ptr->zbuf_size;
    /* libpng is not interested in zstream.data_type */
    /* Set it to a predefined value, to avoid its evaluation inside zlib */
    png_ptr->zstream.data_type = Z_BINARY;

    png_ptr->mode = PNG_HAVE_IHDR;
}

/* Write the palette.  We are careful not to trust png_color to be in the
 * correct order for PNG, so people can redefine it to any convenient
 * structure.
 */
void /* PRIVATE */
png_write_PLTE(png_structp png_ptr, png_colorp palette, png_uint_32 num_pal)
{
    PNG_PLTE;
    png_uint_32 i;
    png_colorp pal_ptr;
    png_byte buf[3];

    png_debug(1, "in png_write_PLTE");

    if ((
            #ifdef PNG_MNG_FEATURES_SUPPORTED
            !(png_ptr->mng_features_permitted & PNG_FLAG_MNG_EMPTY_PLTE) &&
            #endif
            num_pal == 0) || num_pal > 256)
    {
        if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
        {
            png_error(png_ptr, "Invalid number of colors in palette");
        }
        else
        {
            png_warning(png_ptr, "Invalid number of colors in palette");
            return;
        }
    }

    if (!(png_ptr->color_type & PNG_COLOR_MASK_COLOR))
    {
        png_warning(png_ptr,
                    "Ignoring request to write a PLTE chunk in grayscale PNG");
        return;
    }

    png_ptr->num_palette = (png_uint_16)num_pal;
    png_debug1(3, "num_palette = %d", png_ptr->num_palette);

    png_write_chunk_start(png_ptr, (png_bytep)png_PLTE,
                          (png_uint_32)(num_pal * 3));
    #ifdef PNG_POINTER_INDEXING_SUPPORTED
    for (i = 0, pal_ptr = palette; i < num_pal; i++, pal_ptr++)
    {
        buf[0] = pal_ptr->red;
        buf[1] = pal_ptr->green;
        buf[2] = pal_ptr->blue;
        png_write_chunk_data(png_ptr, buf, (png_size_t)3);
    }
    #else
    /* This is a little slower but some buggy compilers need to do this
     * instead
     */
    pal_ptr = palette;
    for (i = 0; i < num_pal; i++)
    {
        buf[0] = pal_ptr[i].red;
        buf[1] = pal_ptr[i].green;
        buf[2] = pal_ptr[i].blue;
        png_write_chunk_data(png_ptr, buf, (png_size_t)3);
    }
    #endif
    png_write_chunk_end(png_ptr);
    png_ptr->mode |= PNG_HAVE_PLTE;
}

/* Write an IDAT chunk */
void /* PRIVATE */
png_write_IDAT(png_structp png_ptr, png_bytep data, png_size_t length)
{
    PNG_IDAT;

    png_debug(1, "in png_write_IDAT");

    /* Optimize the CMF field in the zlib stream. */
    /* This hack of the zlib stream is compliant to the stream specification. */
    if (!(png_ptr->mode & PNG_HAVE_IDAT) &&
        png_ptr->compression_type == PNG_COMPRESSION_TYPE_BASE)
    {
        unsigned int z_cmf = data[0]; /* zlib compression method and flags */
        if ((z_cmf & 0x0f) == 8 && (z_cmf & 0xf0) <= 0x70)
        {
            /* Avoid memory underflows and multiplication overflows.
             *
             * The conditions below are practically always satisfied;
             * however, they still must be checked.
             */
            if (length >= 2 &&
                png_ptr->height < 16384 && png_ptr->width < 16384)
            {
                png_uint_32 uncompressed_idat_size = png_ptr->height *
                                                     ((png_ptr->width *
                                                       png_ptr->channels * png_ptr->bit_depth + 15) >> 3);
                unsigned int z_cinfo = z_cmf >> 4;
                unsigned int half_z_window_size = 1 << (z_cinfo + 7);
                while (uncompressed_idat_size <= half_z_window_size &&
                       half_z_window_size >= 256)
                {
                    z_cinfo--;
                    half_z_window_size >>= 1;
                }
                z_cmf = (z_cmf & 0x0f) | (z_cinfo << 4);
                if (data[0] != (png_byte)z_cmf)
                {
                    data[0] = (png_byte)z_cmf;
                    data[1] &= 0xe0;
                    data[1] += (png_byte)(0x1f - ((z_cmf << 8) + data[1]) % 0x1f);
                }
            }
        }
        else
            png_error(png_ptr,
                      "Invalid zlib compression method or flags in IDAT");
    }

    png_write_chunk(png_ptr, (png_bytep)png_IDAT, data, length);
    png_ptr->mode |= PNG_HAVE_IDAT;
}

/* Write an IEND chunk */
void /* PRIVATE */
png_write_IEND(png_structp png_ptr)
{
    PNG_IEND;

    png_debug(1, "in png_write_IEND");

    png_write_chunk(png_ptr, (png_bytep)png_IEND, NULL,
                    (png_size_t)0);
    png_ptr->mode |= PNG_HAVE_IEND;
}

    #ifdef PNG_WRITE_gAMA_SUPPORTED
/* Write a gAMA chunk */
        #ifdef PNG_FLOATING_POINT_SUPPORTED
void /* PRIVATE */
png_write_gAMA(png_structp png_ptr, double file_gamma)
{
    PNG_gAMA;
    png_uint_32 igamma;
    png_byte buf[4];

    png_debug(1, "in png_write_gAMA");

    /* file_gamma is saved in 1/100,000ths */
    igamma = (png_uint_32)(file_gamma * 100000.0 + 0.5);
    png_save_uint_32(buf, igamma);
    png_write_chunk(png_ptr, (png_bytep)png_gAMA, buf, (png_size_t)4);
}
        #endif
        #ifdef PNG_FIXED_POINT_SUPPORTED
void /* PRIVATE */
png_write_gAMA_fixed(png_structp png_ptr, png_fixed_point file_gamma)
{
    PNG_gAMA;
    png_byte buf[4];

    png_debug(1, "in png_write_gAMA");

    /* file_gamma is saved in 1/100,000ths */
    png_save_uint_32(buf, (png_uint_32)file_gamma);
    png_write_chunk(png_ptr, (png_bytep)png_gAMA, buf, (png_size_t)4);
}
        #endif
    #endif

    #ifdef PNG_WRITE_sRGB_SUPPORTED
/* Write a sRGB chunk */
void /* PRIVATE */
png_write_sRGB(png_structp png_ptr, int srgb_intent)
{
    PNG_sRGB;
    png_byte buf[1];

    png_debug(1, "in png_write_sRGB");

    if (srgb_intent >= PNG_sRGB_INTENT_LAST)
        png_warning(png_ptr,
                    "Invalid sRGB rendering intent specified");
    buf[0] = (png_byte)srgb_intent;
    png_write_chunk(png_ptr, (png_bytep)png_sRGB, buf, (png_size_t)1);
}
    #endif

    #ifdef PNG_WRITE_iCCP_SUPPORTED
/* Write an iCCP chunk */
void /* PRIVATE */
png_write_iCCP(png_structp png_ptr, png_charp name, int compression_type,
               png_charp profile, int profile_len)
{
    PNG_iCCP;
    png_size_t name_len;
    png_charp new_name;
    compression_state comp;
    int embedded_profile_len = 0;

    png_debug(1, "in png_write_iCCP");

    comp.num_output_ptr = 0;
    comp.max_output_ptr = 0;
    comp.output_ptr = NULL;
    comp.input = NULL;
    comp.input_len = 0;

    if ((name_len = png_check_keyword(png_ptr, name,
                                      &new_name)) == 0)
        return;

    if (compression_type != PNG_COMPRESSION_TYPE_BASE)
        png_warning(png_ptr, "Unknown compression type in iCCP chunk");

    if (profile == NULL)
        profile_len = 0;

    if (profile_len > 3)
        embedded_profile_len =
            ((*((png_bytep)profile)) << 24) |
            ((*((png_bytep)profile + 1)) << 16) |
            ((*((png_bytep)profile + 2)) << 8) |
            ((*((png_bytep)profile + 3)));

    if (embedded_profile_len < 0)
    {
        png_warning(png_ptr,
                    "Embedded profile length in iCCP chunk is negative");
        png_free(png_ptr, new_name);
        return;
    }

    if (profile_len < embedded_profile_len)
    {
        png_warning(png_ptr,
                    "Embedded profile length too large in iCCP chunk");
        png_free(png_ptr, new_name);
        return;
    }

    if (profile_len > embedded_profile_len)
    {
        png_warning(png_ptr,
                    "Truncating profile to actual length in iCCP chunk");
        profile_len = embedded_profile_len;
    }

    if (profile_len)
        profile_len = png_text_compress(png_ptr, profile,
                                        (png_size_t)profile_len, PNG_COMPRESSION_TYPE_BASE, &comp);

    /* Make sure we include the NULL after the name and the compression type */
    png_write_chunk_start(png_ptr, (png_bytep)png_iCCP,
                          (png_uint_32)(name_len + profile_len + 2));
    new_name[name_len + 1] = 0x00;
    png_write_chunk_data(png_ptr, (png_bytep)new_name,
                         (png_size_t)(name_len + 2));

    if (profile_len)
        png_write_compressed_data_out(png_ptr, &comp);

    png_write_chunk_end(png_ptr);
    png_free(png_ptr, new_name);
}
    #endif

    #ifdef PNG_WRITE_sPLT_SUPPORTED
/* Write a sPLT chunk */
void /* PRIVATE */
png_write_sPLT(png_structp png_ptr, png_sPLT_tp spalette)
{
    PNG_sPLT;
    png_size_t name_len;
    png_charp new_name;
    png_byte entrybuf[10];
    png_size_t entry_size = (spalette->depth == 8 ? 6 : 10);
    png_size_t palette_size = entry_size * spalette->nentries;
    png_sPLT_entryp ep;
    #ifndef PNG_POINTER_INDEXING_SUPPORTED
    int i;
    #endif

    png_debug(1, "in png_write_sPLT");

    if ((name_len = png_check_keyword(png_ptr, spalette->name, &new_name)) == 0)
        return;

    /* Make sure we include the NULL after the name */
    png_write_chunk_start(png_ptr, (png_bytep)png_sPLT,
                          (png_uint_32)(name_len + 2 + palette_size));
    png_write_chunk_data(png_ptr, (png_bytep)new_name,
                         (png_size_t)(name_len + 1));
    png_write_chunk_data(png_ptr, (png_bytep) & spalette->depth, (png_size_t)1);

    /* Loop through each palette entry, writing appropriately */
    #ifdef PNG_POINTER_INDEXING_SUPPORTED
    for (ep = spalette->entries; ep < spalette->entries + spalette->nentries; ep++)
    {
        if (spalette->depth == 8)
        {
            entrybuf[0] = (png_byte)ep->red;
            entrybuf[1] = (png_byte)ep->green;
            entrybuf[2] = (png_byte)ep->blue;
            entrybuf[3] = (png_byte)ep->alpha;
            png_save_uint_16(entrybuf + 4, ep->frequency);
        }
        else
        {
            png_save_uint_16(entrybuf + 0, ep->red);
            png_save_uint_16(entrybuf + 2, ep->green);
            png_save_uint_16(entrybuf + 4, ep->blue);
            png_save_uint_16(entrybuf + 6, ep->alpha);
            png_save_uint_16(entrybuf + 8, ep->frequency);
        }
        png_write_chunk_data(png_ptr, entrybuf, (png_size_t)entry_size);
    }
    #else
    ep = spalette->entries;
    for (i = 0; i > spalette->nentries; i++)
    {
        if (spalette->depth == 8)
        {
            entrybuf[0] = (png_byte)ep[i].red;
            entrybuf[1] = (png_byte)ep[i].green;
            entrybuf[2] = (png_byte)ep[i].blue;
            entrybuf[3] = (png_byte)ep[i].alpha;
            png_save_uint_16(entrybuf + 4, ep[i].frequency);
        }
        else
        {
            png_save_uint_16(entrybuf + 0, ep[i].red);
            png_save_uint_16(entrybuf + 2, ep[i].green);
            png_save_uint_16(entrybuf + 4, ep[i].blue);
            png_save_uint_16(entrybuf + 6, ep[i].alpha);
            png_save_uint_16(entrybuf + 8, ep[i].frequency);
        }
        png_write_chunk_data(png_ptr, entrybuf, (png_size_t)entry_size);
    }
    #endif

    png_write_chunk_end(png_ptr);
    png_free(png_ptr, new_name);
}
    #endif

    #ifdef PNG_WRITE_sBIT_SUPPORTED
/* Write the sBIT chunk */
void /* PRIVATE */
png_write_sBIT(png_structp png_ptr, png_color_8p sbit, int color_type)
{
    PNG_sBIT;
    png_byte buf[4];
    png_size_t size;

    png_debug(1, "in png_write_sBIT");

    /* Make sure we don't depend upon the order of PNG_COLOR_8 */
    if (color_type & PNG_COLOR_MASK_COLOR)
    {
        png_byte maxbits;

        maxbits = (png_byte)(color_type == PNG_COLOR_TYPE_PALETTE ? 8 :
                             png_ptr->usr_bit_depth);
        if (sbit->red == 0 || sbit->red > maxbits ||
            sbit->green == 0 || sbit->green > maxbits ||
            sbit->blue == 0 || sbit->blue > maxbits)
        {
            png_warning(png_ptr, "Invalid sBIT depth specified");
            return;
        }
        buf[0] = sbit->red;
        buf[1] = sbit->green;
        buf[2] = sbit->blue;
        size = 3;
    }
    else
    {
        if (sbit->gray == 0 || sbit->gray > png_ptr->usr_bit_depth)
        {
            png_warning(png_ptr, "Invalid sBIT depth specified");
            return;
        }
        buf[0] = sbit->gray;
        size = 1;
    }

    if (color_type & PNG_COLOR_MASK_ALPHA)
    {
        if (sbit->alpha == 0 || sbit->alpha > png_ptr->usr_bit_depth)
        {
            png_warning(png_ptr, "Invalid sBIT depth specified");
            return;
        }
        buf[size++] = sbit->alpha;
    }

    png_write_chunk(png_ptr, (png_bytep)png_sBIT, buf, size);
}
    #endif

    #ifdef PNG_WRITE_cHRM_SUPPORTED
/* Write the cHRM chunk */
        #ifdef PNG_FLOATING_POINT_SUPPORTED
void /* PRIVATE */
png_write_cHRM(png_structp png_ptr, double white_x, double white_y,
               double red_x, double red_y, double green_x, double green_y,
               double blue_x, double blue_y)
{
    PNG_cHRM;
    png_byte buf[32];

    png_fixed_point int_white_x, int_white_y, int_red_x, int_red_y,
                    int_green_x, int_green_y, int_blue_x, int_blue_y;

    png_debug(1, "in png_write_cHRM");

    int_white_x = (png_uint_32)(white_x * 100000.0 + 0.5);
    int_white_y = (png_uint_32)(white_y * 100000.0 + 0.5);
    int_red_x = (png_uint_32)(red_x * 100000.0 + 0.5);
    int_red_y = (png_uint_32)(red_y * 100000.0 + 0.5);
    int_green_x = (png_uint_32)(green_x * 100000.0 + 0.5);
    int_green_y = (png_uint_32)(green_y * 100000.0 + 0.5);
    int_blue_x = (png_uint_32)(blue_x * 100000.0 + 0.5);
    int_blue_y = (png_uint_32)(blue_y * 100000.0 + 0.5);

    #ifdef PNG_CHECK_cHRM_SUPPORTED
    if (png_check_cHRM_fixed(png_ptr, int_white_x, int_white_y,
                             int_red_x, int_red_y, int_green_x, int_green_y, int_blue_x, int_blue_y))
    #endif
    {
        /* Each value is saved in 1/100,000ths */

        png_save_uint_32(buf, int_white_x);
        png_save_uint_32(buf + 4, int_white_y);

        png_save_uint_32(buf + 8, int_red_x);
        png_save_uint_32(buf + 12, int_red_y);

        png_save_uint_32(buf + 16, int_green_x);
        png_save_uint_32(buf + 20, int_green_y);

        png_save_uint_32(buf + 24, int_blue_x);
        png_save_uint_32(buf + 28, int_blue_y);

        png_write_chunk(png_ptr, (png_bytep)png_cHRM, buf, (png_size_t)32);
    }
}
        #endif
        #ifdef PNG_FIXED_POINT_SUPPORTED
void /* PRIVATE */
png_write_cHRM_fixed(png_structp png_ptr, png_fixed_point white_x,
                     png_fixed_point white_y, png_fixed_point red_x, png_fixed_point red_y,
                     png_fixed_point green_x, png_fixed_point green_y, png_fixed_point blue_x,
                     png_fixed_point blue_y)
{
    PNG_cHRM;
    png_byte buf[32];

    png_debug(1, "in png_write_cHRM");

    /* Each value is saved in 1/100,000ths */
    #ifdef PNG_CHECK_cHRM_SUPPORTED
    if (png_check_cHRM_fixed(png_ptr, white_x, white_y, red_x, red_y,
                             green_x, green_y, blue_x, blue_y))
    #endif
    {
        png_save_uint_32(buf, (png_uint_32)white_x);
        png_save_uint_32(buf + 4, (png_uint_32)white_y);

        png_save_uint_32(buf + 8, (png_uint_32)red_x);
        png_save_uint_32(buf + 12, (png_uint_32)red_y);

        png_save_uint_32(buf + 16, (png_uint_32)green_x);
        png_save_uint_32(buf + 20, (png_uint_32)green_y);

        png_save_uint_32(buf + 24, (png_uint_32)blue_x);
        png_save_uint_32(buf + 28, (png_uint_32)blue_y);

        png_write_chunk(png_ptr, (png_bytep)png_cHRM, buf, (png_size_t)32);
    }
}
        #endif
    #endif

    #ifdef PNG_WRITE_tRNS_SUPPORTED
/* Write the tRNS chunk */
void /* PRIVATE */
png_write_tRNS(png_structp png_ptr, png_bytep trans_alpha, png_color_16p tran,
               int num_trans, int color_type)
{
    PNG_tRNS;
    png_byte buf[6];

    png_debug(1, "in png_write_tRNS");

    if (color_type == PNG_COLOR_TYPE_PALETTE)
    {
        if (num_trans <= 0 || num_trans > (int)png_ptr->num_palette)
        {
            png_warning(png_ptr, "Invalid number of transparent colors specified");
            return;
        }
        /* Write the chunk out as it is */
        png_write_chunk(png_ptr, (png_bytep)png_tRNS, trans_alpha,
                        (png_size_t)num_trans);
    }
    else if (color_type == PNG_COLOR_TYPE_GRAY)
    {
        /* One 16 bit value */
        if (tran->gray >= (1 << png_ptr->bit_depth))
        {
            png_warning(png_ptr,
                        "Ignoring attempt to write tRNS chunk out-of-range for bit_depth");
            return;
        }
        png_save_uint_16(buf, tran->gray);
        png_write_chunk(png_ptr, (png_bytep)png_tRNS, buf, (png_size_t)2);
    }
    else if (color_type == PNG_COLOR_TYPE_RGB)
    {
        /* Three 16 bit values */
        png_save_uint_16(buf, tran->red);
        png_save_uint_16(buf + 2, tran->green);
        png_save_uint_16(buf + 4, tran->blue);
        if (png_ptr->bit_depth == 8 && (buf[0] | buf[2] | buf[4]))
        {
            png_warning(png_ptr,
                        "Ignoring attempt to write 16-bit tRNS chunk when bit_depth is 8");
            return;
        }
        png_write_chunk(png_ptr, (png_bytep)png_tRNS, buf, (png_size_t)6);
    }
    else
    {
        png_warning(png_ptr, "Can't write tRNS with an alpha channel");
    }
}
    #endif

    #ifdef PNG_WRITE_bKGD_SUPPORTED
/* Write the background chunk */
void /* PRIVATE */
png_write_bKGD(png_structp png_ptr, png_color_16p back, int color_type)
{
    PNG_bKGD;
    png_byte buf[6];

    png_debug(1, "in png_write_bKGD");

    if (color_type == PNG_COLOR_TYPE_PALETTE)
    {
        if (
            #ifdef PNG_MNG_FEATURES_SUPPORTED
                (png_ptr->num_palette ||
                (!(png_ptr->mng_features_permitted & PNG_FLAG_MNG_EMPTY_PLTE))) &&
            #endif
            back->index >= png_ptr->num_palette)
        {
            png_warning(png_ptr, "Invalid background palette index");
            return;
        }
        buf[0] = back->index;
        png_write_chunk(png_ptr, (png_bytep)png_bKGD, buf, (png_size_t)1);
    }
    else if (color_type & PNG_COLOR_MASK_COLOR)
    {
        png_save_uint_16(buf, back->red);
        png_save_uint_16(buf + 2, back->green);
        png_save_uint_16(buf + 4, back->blue);
        if (png_ptr->bit_depth == 8 && (buf[0] | buf[2] | buf[4]))
        {
            png_warning(png_ptr,
                        "Ignoring attempt to write 16-bit bKGD chunk when bit_depth is 8");
            return;
        }
        png_write_chunk(png_ptr, (png_bytep)png_bKGD, buf, (png_size_t)6);
    }
    else
    {
        if (back->gray >= (1 << png_ptr->bit_depth))
        {
            png_warning(png_ptr,
                        "Ignoring attempt to write bKGD chunk out-of-range for bit_depth");
            return;
        }
        png_save_uint_16(buf, back->gray);
        png_write_chunk(png_ptr, (png_bytep)png_bKGD, buf, (png_size_t)2);
    }
}
    #endif

    #ifdef PNG_WRITE_hIST_SUPPORTED
/* Write the histogram */
void /* PRIVATE */
png_write_hIST(png_structp png_ptr, png_uint_16p hist, int num_hist)
{
    PNG_hIST;
    int i;
    png_byte buf[3];

    png_debug(1, "in png_write_hIST");

    if (num_hist > (int)png_ptr->num_palette)
    {
        png_debug2(3, "num_hist = %d, num_palette = %d", num_hist,
                   png_ptr->num_palette);
        png_warning(png_ptr, "Invalid number of histogram entries specified");
        return;
    }

    png_write_chunk_start(png_ptr, (png_bytep)png_hIST,
                          (png_uint_32)(num_hist * 2));
    for (i = 0; i < num_hist; i++)
    {
        png_save_uint_16(buf, hist[i]);
        png_write_chunk_data(png_ptr, buf, (png_size_t)2);
    }
    png_write_chunk_end(png_ptr);
}
    #endif

    #if defined (PNG_WRITE_TEXT_SUPPORTED) || defined (PNG_WRITE_pCAL_SUPPORTED) || \
    defined (PNG_WRITE_iCCP_SUPPORTED) || defined (PNG_WRITE_sPLT_SUPPORTED)
/* Check that the tEXt or zTXt keyword is valid per PNG 1.0 specification,
 * and if invalid, correct the keyword rather than discarding the entire
 * chunk.  The PNG 1.0 specification requires keywords 1-79 characters in
 * length, forbids leading or trailing whitespace, multiple internal spaces,
 * and the non-break space (0x80) from ISO 8859-1.  Returns keyword length.
 *
 * The new_key is allocated to hold the corrected keyword and must be freed
 * by the calling routine.  This avoids problems with trying to write to
 * static keywords without having to have duplicate copies of the strings.
 */
png_size_t /* PRIVATE */
png_check_keyword(png_structp png_ptr, png_charp key, png_charpp new_key)
{
    png_size_t key_len;
    png_charp kp, dp;
    int kflag;
    int kwarn = 0;

    png_debug(1, "in png_check_keyword");

    *new_key = NULL;

    if (key == NULL || (key_len = png_strlen(key)) == 0)
    {
        png_warning(png_ptr, "zero length keyword");
        return ((png_size_t)0);
    }

    png_debug1(2, "Keyword to be checked is '%s'", key);

    *new_key = (png_charp)png_malloc_warn(png_ptr, (png_uint_32)(key_len + 2));
    if (*new_key == NULL)
    {
        png_warning(png_ptr, "Out of memory while procesing keyword");
        return ((png_size_t)0);
    }

    /* Replace non-printing characters with a blank and print a warning */
    for (kp = key, dp = *new_key; *kp != '\0'; kp++, dp++)
    {
        if ((png_byte) * kp < 0x20 ||
            ((png_byte) * kp > 0x7E && (png_byte) * kp < 0xA1))
        {
            #ifdef PNG_STDIO_SUPPORTED
            char msg[40];

            png_snprintf(msg, 40,
                         "invalid keyword character 0x%02X", (png_byte) * kp);
            png_warning(png_ptr, msg);
            #else
            png_warning(png_ptr, "invalid character in keyword");
            #endif
            *dp = ' ';
        }
        else
        {
            *dp = *kp;
        }
    }
    *dp = '\0';

    /* Remove any trailing white space. */
    kp = *new_key + key_len - 1;
    if (*kp == ' ')
    {
        png_warning(png_ptr, "trailing spaces removed from keyword");

        while (*kp == ' ')
        {
            *(kp--) = '\0';
            key_len--;
        }
    }

    /* Remove any leading white space. */
    kp = *new_key;
    if (*kp == ' ')
    {
        png_warning(png_ptr, "leading spaces removed from keyword");

        while (*kp == ' ')
        {
            kp++;
            key_len--;
        }
    }

    png_debug1(2, "Checking for multiple internal spaces in '%s'", kp);

    /* Remove multiple internal spaces. */
    for (kflag = 0, dp = *new_key; *kp != '\0'; kp++)
    {
        if (*kp == ' ' && kflag == 0)
        {
            *(dp++) = *kp;
            kflag = 1;
        }
        else if (*kp == ' ')
        {
            key_len--;
            kwarn = 1;
        }
        else
        {
            *(dp++) = *kp;
            kflag = 0;
        }
    }
    *dp = '\0';
    if (kwarn)
        png_warning(png_ptr, "extra interior spaces removed from keyword");

    if (key_len == 0)
    {
        png_free(png_ptr, *new_key);
        png_warning(png_ptr, "Zero length keyword");
    }

    if (key_len > 79)
    {
        png_warning(png_ptr, "keyword length must be 1 - 79 characters");
        (*new_key)[79] = '\0';
        key_len = 79;
    }

    return (key_len);
}
    #endif

    #ifdef PNG_WRITE_tEXt_SUPPORTED
/* Write a tEXt chunk */
void /* PRIVATE */
png_write_tEXt(png_structp png_ptr, png_charp key, png_charp text,
               png_size_t text_len)
{
    PNG_tEXt;
    png_size_t key_len;
    png_charp new_key;

    png_debug(1, "in png_write_tEXt");

    if ((key_len = png_check_keyword(png_ptr, key, &new_key)) == 0)
        return;

    if (text == NULL || *text == '\0')
        text_len = 0;
    else
        text_len = png_strlen(text);

    /* Make sure we include the 0 after the key */
    png_write_chunk_start(png_ptr, (png_bytep)png_tEXt,
                          (png_uint_32)(key_len + text_len + 1));
    /*
     * We leave it to the application to meet PNG-1.0 requirements on the
     * contents of the text.  PNG-1.0 through PNG-1.2 discourage the use of
     * any non-Latin-1 characters except for NEWLINE.  ISO PNG will forbid them.
     * The NUL character is forbidden by PNG-1.0 through PNG-1.2 and ISO PNG.
     */
    png_write_chunk_data(png_ptr, (png_bytep)new_key,
                         (png_size_t)(key_len + 1));
    if (text_len)
        png_write_chunk_data(png_ptr, (png_bytep)text, (png_size_t)text_len);

    png_write_chunk_end(png_ptr);
    png_free(png_ptr, new_key);
}
    #endif

    #ifdef PNG_WRITE_zTXt_SUPPORTED
/* Write a compressed text chunk */
void /* PRIVATE */
png_write_zTXt(png_structp png_ptr, png_charp key, png_charp text,
               png_size_t text_len, int compression)
{
    PNG_zTXt;
    png_size_t key_len;
    char buf[1];
    png_charp new_key;
    compression_state comp;

    png_debug(1, "in png_write_zTXt");

    comp.num_output_ptr = 0;
    comp.max_output_ptr = 0;
    comp.output_ptr = NULL;
    comp.input = NULL;
    comp.input_len = 0;

    if ((key_len = png_check_keyword(png_ptr, key, &new_key)) == 0)
    {
        png_free(png_ptr, new_key);
        return;
    }

    if (text == NULL || *text == '\0' || compression == PNG_TEXT_COMPRESSION_NONE)
    {
        png_write_tEXt(png_ptr, new_key, text, (png_size_t)0);
        png_free(png_ptr, new_key);
        return;
    }

    text_len = png_strlen(text);

    /* Compute the compressed data; do it now for the length */
    text_len = png_text_compress(png_ptr, text, text_len, compression,
                                 &comp);

    /* Write start of chunk */
    png_write_chunk_start(png_ptr, (png_bytep)png_zTXt,
                          (png_uint_32)(key_len + text_len + 2));
    /* Write key */
    png_write_chunk_data(png_ptr, (png_bytep)new_key,
                         (png_size_t)(key_len + 1));
    png_free(png_ptr, new_key);

    buf[0] = (png_byte)compression;
    /* Write compression */
    png_write_chunk_data(png_ptr, (png_bytep)buf, (png_size_t)1);
    /* Write the compressed data */
    png_write_compressed_data_out(png_ptr, &comp);

    /* Close the chunk */
    png_write_chunk_end(png_ptr);
}
    #endif

    #ifdef PNG_WRITE_iTXt_SUPPORTED
/* Write an iTXt chunk */
void /* PRIVATE */
png_write_iTXt(png_structp png_ptr, int compression, png_charp key,
               png_charp lang, png_charp lang_key, png_charp text)
{
    PNG_iTXt;
    png_size_t lang_len, key_len, lang_key_len, text_len;
    png_charp new_lang;
    png_charp new_key = NULL;
    png_byte cbuf[2];
    compression_state comp;

    png_debug(1, "in png_write_iTXt");

    comp.num_output_ptr = 0;
    comp.max_output_ptr = 0;
    comp.output_ptr = NULL;
    comp.input = NULL;

    if ((key_len = png_check_keyword(png_ptr, key, &new_key)) == 0)
        return;

    if ((lang_len = png_check_keyword(png_ptr, lang, &new_lang)) == 0)
    {
        png_warning(png_ptr, "Empty language field in iTXt chunk");
        new_lang = NULL;
        lang_len = 0;
    }

    if (lang_key == NULL)
        lang_key_len = 0;
    else
        lang_key_len = png_strlen(lang_key);

    if (text == NULL)
        text_len = 0;
    else
        text_len = png_strlen(text);

    /* Compute the compressed data; do it now for the length */
    text_len = png_text_compress(png_ptr, text, text_len, compression - 2,
                                 &comp);


    /* Make sure we include the compression flag, the compression byte,
     * and the NULs after the key, lang, and lang_key parts */

    png_write_chunk_start(png_ptr, (png_bytep)png_iTXt,
                          (png_uint_32)(
                              5 /* comp byte, comp flag, terminators for key, lang and lang_key */
                              + key_len
                              + lang_len
                              + lang_key_len
                              + text_len));

    /* We leave it to the application to meet PNG-1.0 requirements on the
     * contents of the text.  PNG-1.0 through PNG-1.2 discourage the use of
     * any non-Latin-1 characters except for NEWLINE.  ISO PNG will forbid them.
     * The NUL character is forbidden by PNG-1.0 through PNG-1.2 and ISO PNG.
     */
    png_write_chunk_data(png_ptr, (png_bytep)new_key,
                         (png_size_t)(key_len + 1));

    /* Set the compression flag */
    if (compression == PNG_ITXT_COMPRESSION_NONE || \
        compression == PNG_TEXT_COMPRESSION_NONE)
        cbuf[0] = 0;
    else /* compression == PNG_ITXT_COMPRESSION_zTXt */
        cbuf[0] = 1;
    /* Set the compression method */
    cbuf[1] = 0;
    png_write_chunk_data(png_ptr, cbuf, (png_size_t)2);

    cbuf[0] = 0;
    png_write_chunk_data(png_ptr, (new_lang ? (png_bytep)new_lang : cbuf),
                         (png_size_t)(lang_len + 1));
    png_write_chunk_data(png_ptr, (lang_key ? (png_bytep)lang_key : cbuf),
                         (png_size_t)(lang_key_len + 1));
    png_write_compressed_data_out(png_ptr, &comp);

    png_write_chunk_end(png_ptr);
    png_free(png_ptr, new_key);
    png_free(png_ptr, new_lang);
}
    #endif

    #ifdef PNG_WRITE_oFFs_SUPPORTED
/* Write the oFFs chunk */
void /* PRIVATE */
png_write_oFFs(png_structp png_ptr, png_int_32 x_offset, png_int_32 y_offset,
               int unit_type)
{
    PNG_oFFs;
    png_byte buf[9];

    png_debug(1, "in png_write_oFFs");

    if (unit_type >= PNG_OFFSET_LAST)
        png_warning(png_ptr, "Unrecognized unit type for oFFs chunk");

    png_save_int_32(buf, x_offset);
    png_save_int_32(buf + 4, y_offset);
    buf[8] = (png_byte)unit_type;

    png_write_chunk(png_ptr, (png_bytep)png_oFFs, buf, (png_size_t)9);
}
    #endif
    #ifdef PNG_WRITE_pCAL_SUPPORTED
/* Write the pCAL chunk (described in the PNG extensions document) */
void /* PRIVATE */
png_write_pCAL(png_structp png_ptr, png_charp purpose, png_int_32 X0,
               png_int_32 X1, int type, int nparams, png_charp units, png_charpp params)
{
    PNG_pCAL;
    png_size_t purpose_len, units_len, total_len;
    png_uint_32p params_len;
    png_byte buf[10];
    png_charp new_purpose;
    int i;

    png_debug1(1, "in png_write_pCAL (%d parameters)", nparams);

    if (type >= PNG_EQUATION_LAST)
        png_warning(png_ptr, "Unrecognized equation type for pCAL chunk");

    purpose_len = png_check_keyword(png_ptr, purpose, &new_purpose) + 1;
    png_debug1(3, "pCAL purpose length = %d", (int)purpose_len);
    units_len = png_strlen(units) + (nparams == 0 ? 0 : 1);
    png_debug1(3, "pCAL units length = %d", (int)units_len);
    total_len = purpose_len + units_len + 10;

    params_len = (png_uint_32p)png_malloc(png_ptr,
                                          (png_alloc_size_t)(nparams * png_sizeof(png_uint_32)));

    /* Find the length of each parameter, making sure we don't count the
       null terminator for the last parameter. */
    for (i = 0; i < nparams; i++)
    {
        params_len[i] = png_strlen(params[i]) + (i == nparams - 1 ? 0 : 1);
        png_debug2(3, "pCAL parameter %d length = %lu", i,
                   (unsigned long)params_len[i]);
        total_len += (png_size_t)params_len[i];
    }

    png_debug1(3, "pCAL total length = %d", (int)total_len);
    png_write_chunk_start(png_ptr, (png_bytep)png_pCAL, (png_uint_32)total_len);
    png_write_chunk_data(png_ptr, (png_bytep)new_purpose,
                         (png_size_t)purpose_len);
    png_save_int_32(buf, X0);
    png_save_int_32(buf + 4, X1);
    buf[8] = (png_byte)type;
    buf[9] = (png_byte)nparams;
    png_write_chunk_data(png_ptr, buf, (png_size_t)10);
    png_write_chunk_data(png_ptr, (png_bytep)units, (png_size_t)units_len);

    png_free(png_ptr, new_purpose);

    for (i = 0; i < nparams; i++)
    {
        png_write_chunk_data(png_ptr, (png_bytep)params[i],
                             (png_size_t)params_len[i]);
    }

    png_free(png_ptr, params_len);
    png_write_chunk_end(png_ptr);
}
    #endif

    #ifdef PNG_WRITE_sCAL_SUPPORTED
/* Write the sCAL chunk */
        #if defined (PNG_FLOATING_POINT_SUPPORTED) && defined (PNG_STDIO_SUPPORTED)
void /* PRIVATE */
png_write_sCAL(png_structp png_ptr, int unit, double width, double height)
{
    PNG_sCAL;
    char buf[64];
    png_size_t total_len;

    png_debug(1, "in png_write_sCAL");

    buf[0] = (char)unit;
    png_snprintf(buf + 1, 63, "%12.12e", width);
    total_len = 1 + png_strlen(buf + 1) + 1;
    png_snprintf(buf + total_len, 64 - total_len, "%12.12e", height);
    total_len += png_strlen(buf + total_len);

    png_debug1(3, "sCAL total length = %u", (unsigned int)total_len);
    png_write_chunk(png_ptr, (png_bytep)png_sCAL, (png_bytep)buf, total_len);
}
        #else
            #ifdef PNG_FIXED_POINT_SUPPORTED
void /* PRIVATE */
png_write_sCAL_s(png_structp png_ptr, int unit, png_charp width,
                 png_charp height)
{
    PNG_sCAL;
    png_byte buf[64];
    png_size_t wlen, hlen, total_len;

    png_debug(1, "in png_write_sCAL_s");

    wlen = png_strlen(width);
    hlen = png_strlen(height);
    total_len = wlen + hlen + 2;
    if (total_len > 64)
    {
        png_warning(png_ptr, "Can't write sCAL (buffer too small)");
        return;
    }

    buf[0] = (png_byte)unit;
    png_memcpy(buf + 1, width, wlen + 1);     /* Append the '\0' here */
    png_memcpy(buf + wlen + 2, height, hlen); /* Do NOT append the '\0' here */

    png_debug1(3, "sCAL total length = %u", (unsigned int)total_len);
    png_write_chunk(png_ptr, (png_bytep)png_sCAL, buf, total_len);
}
            #endif
        #endif
    #endif

    #ifdef PNG_WRITE_pHYs_SUPPORTED
/* Write the pHYs chunk */
void /* PRIVATE */
png_write_pHYs(png_structp png_ptr, png_uint_32 x_pixels_per_unit,
               png_uint_32 y_pixels_per_unit,
               int unit_type)
{
    PNG_pHYs;
    png_byte buf[9];

    png_debug(1, "in png_write_pHYs");

    if (unit_type >= PNG_RESOLUTION_LAST)
        png_warning(png_ptr, "Unrecognized unit type for pHYs chunk");

    png_save_uint_32(buf, x_pixels_per_unit);
    png_save_uint_32(buf + 4, y_pixels_per_unit);
    buf[8] = (png_byte)unit_type;

    png_write_chunk(png_ptr, (png_bytep)png_pHYs, buf, (png_size_t)9);
}
    #endif

    #ifdef PNG_WRITE_tIME_SUPPORTED
/* Write the tIME chunk.  Use either png_convert_from_struct_tm()
 * or png_convert_from_time_t(), or fill in the structure yourself.
 */
void /* PRIVATE */
png_write_tIME(png_structp png_ptr, png_timep mod_time)
{
    PNG_tIME;
    png_byte buf[7];

    png_debug(1, "in png_write_tIME");

    if (mod_time->month > 12 || mod_time->month < 1 ||
        mod_time->day > 31 || mod_time->day < 1 ||
        mod_time->hour > 23 || mod_time->second > 60)
    {
        png_warning(png_ptr, "Invalid time specified for tIME chunk");
        return;
    }

    png_save_uint_16(buf, mod_time->year);
    buf[2] = mod_time->month;
    buf[3] = mod_time->day;
    buf[4] = mod_time->hour;
    buf[5] = mod_time->minute;
    buf[6] = mod_time->second;

    png_write_chunk(png_ptr, (png_bytep)png_tIME, buf, (png_size_t)7);
}
    #endif

/* Initializes the row writing capability of libpng */
void /* PRIVATE */
png_write_start_row(png_structp png_ptr)
{
    #ifdef PNG_WRITE_INTERLACING_SUPPORTED
    /* Arrays to facilitate easy interlacing - use pass (0 - 6) as index */

    /* Start of interlace block */
    int png_pass_start[7] = { 0, 4, 0, 2, 0, 1, 0 };

    /* Offset to next interlace block */
    int png_pass_inc[7] = { 8, 8, 4, 4, 2, 2, 1 };

    /* Start of interlace block in the y direction */
    int png_pass_ystart[7] = { 0, 0, 4, 0, 2, 0, 1 };

    /* Offset to next interlace block in the y direction */
    int png_pass_yinc[7] = { 8, 8, 8, 4, 4, 2, 2 };
    #endif

    png_size_t buf_size;

    png_debug(1, "in png_write_start_row");

    buf_size = (png_size_t)(PNG_ROWBYTES(
                                png_ptr->usr_channels * png_ptr->usr_bit_depth, png_ptr->width) + 1);

    /* Set up row buffer */
    png_ptr->row_buf = (png_bytep)png_malloc(png_ptr,
                                             (png_alloc_size_t)buf_size);
    png_ptr->row_buf[0] = PNG_FILTER_VALUE_NONE;

    #ifdef PNG_WRITE_FILTER_SUPPORTED
    /* Set up filtering buffer, if using this filter */
    if (png_ptr->do_filter & PNG_FILTER_SUB)
    {
        png_ptr->sub_row = (png_bytep)png_malloc(png_ptr,
                                                 (png_alloc_size_t)(png_ptr->rowbytes + 1));
        png_ptr->sub_row[0] = PNG_FILTER_VALUE_SUB;
    }

    /* We only need to keep the previous row if we are using one of these. */
    if (png_ptr->do_filter & (PNG_FILTER_AVG | PNG_FILTER_UP | PNG_FILTER_PAETH))
    {
        /* Set up previous row buffer */
        png_ptr->prev_row = (png_bytep)png_calloc(png_ptr,
                                                  (png_alloc_size_t)buf_size);

        if (png_ptr->do_filter & PNG_FILTER_UP)
        {
            png_ptr->up_row = (png_bytep)png_malloc(png_ptr,
                                                    (png_size_t)(png_ptr->rowbytes + 1));
            png_ptr->up_row[0] = PNG_FILTER_VALUE_UP;
        }

        if (png_ptr->do_filter & PNG_FILTER_AVG)
        {
            png_ptr->avg_row = (png_bytep)png_malloc(png_ptr,
                                                     (png_alloc_size_t)(png_ptr->rowbytes + 1));
            png_ptr->avg_row[0] = PNG_FILTER_VALUE_AVG;
        }

        if (png_ptr->do_filter & PNG_FILTER_PAETH)
        {
            png_ptr->paeth_row = (png_bytep)png_malloc(png_ptr,
                                                       (png_size_t)(png_ptr->rowbytes + 1));
            png_ptr->paeth_row[0] = PNG_FILTER_VALUE_PAETH;
        }
    }
    #endif /* PNG_WRITE_FILTER_SUPPORTED */

    #ifdef PNG_WRITE_INTERLACING_SUPPORTED
    /* If interlaced, we need to set up width and height of pass */
    if (png_ptr->interlaced)
    {
        if (!(png_ptr->transformations & PNG_INTERLACE))
        {
            png_ptr->num_rows = (png_ptr->height + png_pass_yinc[0] - 1 -
                                 png_pass_ystart[0]) / png_pass_yinc[0];
            png_ptr->usr_width = (png_ptr->width + png_pass_inc[0] - 1 -
                                  png_pass_start[0]) / png_pass_inc[0];
        }
        else
        {
            png_ptr->num_rows = png_ptr->height;
            png_ptr->usr_width = png_ptr->width;
        }
    }
    else
    #endif
    {
        png_ptr->num_rows = png_ptr->height;
        png_ptr->usr_width = png_ptr->width;
    }
    png_ptr->zstream.avail_out = (uInt)png_ptr->zbuf_size;
    png_ptr->zstream.next_out = png_ptr->zbuf;
}

/* Internal use only.  Called when finished processing a row of data. */
void /* PRIVATE */
png_write_finish_row(png_structp png_ptr)
{
    #ifdef PNG_WRITE_INTERLACING_SUPPORTED
    /* Arrays to facilitate easy interlacing - use pass (0 - 6) as index */

    /* Start of interlace block */
    int png_pass_start[7] = { 0, 4, 0, 2, 0, 1, 0 };

    /* Offset to next interlace block */
    int png_pass_inc[7] = { 8, 8, 4, 4, 2, 2, 1 };

    /* Start of interlace block in the y direction */
    int png_pass_ystart[7] = { 0, 0, 4, 0, 2, 0, 1 };

    /* Offset to next interlace block in the y direction */
    int png_pass_yinc[7] = { 8, 8, 8, 4, 4, 2, 2 };
    #endif

    int ret;

    png_debug(1, "in png_write_finish_row");

    /* Next row */
    png_ptr->row_number++;

    /* See if we are done */
    if (png_ptr->row_number < png_ptr->num_rows)
        return;

    #ifdef PNG_WRITE_INTERLACING_SUPPORTED
    /* If interlaced, go to next pass */
    if (png_ptr->interlaced)
    {
        png_ptr->row_number = 0;
        if (png_ptr->transformations & PNG_INTERLACE)
        {
            png_ptr->pass++;
        }
        else
        {
            /* Loop until we find a non-zero width or height pass */
            do
            {
                png_ptr->pass++;
                if (png_ptr->pass >= 7)
                    break;
                png_ptr->usr_width = (png_ptr->width +
                                      png_pass_inc[png_ptr->pass] - 1 -
                                      png_pass_start[png_ptr->pass]) /
                                     png_pass_inc[png_ptr->pass];
                png_ptr->num_rows = (png_ptr->height +
                                     png_pass_yinc[png_ptr->pass] - 1 -
                                     png_pass_ystart[png_ptr->pass]) /
                                    png_pass_yinc[png_ptr->pass];
                if (png_ptr->transformations & PNG_INTERLACE)
                    break;
            }
            while (png_ptr->usr_width == 0 || png_ptr->num_rows == 0);

        }

        /* Reset the row above the image for the next pass */
        if (png_ptr->pass < 7)
        {
            if (png_ptr->prev_row != NULL)
                png_memset(png_ptr->prev_row, 0,
                           (png_size_t)(PNG_ROWBYTES(png_ptr->usr_channels *
                                                     png_ptr->usr_bit_depth, png_ptr->width)) + 1);
            return;
        }
    }
    #endif

    /* If we get here, we've just written the last row, so we need
       to flush the compressor */
    do
    {
        /* Tell the compressor we are done */
        ret = deflate(&png_ptr->zstream, Z_FINISH);
        /* Check for an error */
        if (ret == Z_OK)
        {
            /* Check to see if we need more room */
            if (!(png_ptr->zstream.avail_out))
            {
                png_write_IDAT(png_ptr, png_ptr->zbuf, png_ptr->zbuf_size);
                png_ptr->zstream.next_out = png_ptr->zbuf;
                png_ptr->zstream.avail_out = (uInt)png_ptr->zbuf_size;
            }
        }
        else if (ret != Z_STREAM_END)
        {
            if (png_ptr->zstream.msg != NULL)
                png_error(png_ptr, png_ptr->zstream.msg);
            else
                png_error(png_ptr, "zlib error");
        }
    }
    while (ret != Z_STREAM_END);

    /* Write any extra space */
    if (png_ptr->zstream.avail_out < png_ptr->zbuf_size)
    {
        png_write_IDAT(png_ptr, png_ptr->zbuf, png_ptr->zbuf_size -
                       png_ptr->zstream.avail_out);
    }

    deflateReset(&png_ptr->zstream);
    png_ptr->zstream.data_type = Z_BINARY;
}

    #ifdef PNG_WRITE_INTERLACING_SUPPORTED
/* Pick out the correct pixels for the interlace pass.
 * The basic idea here is to go through the row with a source
 * pointer and a destination pointer (sp and dp), and copy the
 * correct pixels for the pass.  As the row gets compacted,
 * sp will always be >= dp, so we should never overwrite anything.
 * See the default: case for the easiest code to understand.
 */
void /* PRIVATE */
png_do_write_interlace(png_row_infop row_info, png_bytep row, int pass)
{
    /* Arrays to facilitate easy interlacing - use pass (0 - 6) as index */

    /* Start of interlace block */
    int png_pass_start[7] = { 0, 4, 0, 2, 0, 1, 0 };

    /* Offset to next interlace block */
    int png_pass_inc[7] = { 8, 8, 4, 4, 2, 2, 1 };

    png_debug(1, "in png_do_write_interlace");

    /* We don't have to do anything on the last pass (6) */
    if (pass < 6)
    {
        /* Each pixel depth is handled separately */
        switch (row_info->pixel_depth)
        {
            case 1:
            {
                png_bytep sp;
                png_bytep dp;
                int shift;
                int d;
                int value;
                png_uint_32 i;
                png_uint_32 row_width = row_info->width;

                dp = row;
                d = 0;
                shift = 7;
                for (i = png_pass_start[pass]; i < row_width;
                     i += png_pass_inc[pass])
                {
                    sp = row + (png_size_t)(i >> 3);
                    value = (int)(*sp >> (7 - (int)(i & 0x07))) & 0x01;
                    d |= (value << shift);

                    if (shift == 0)
                    {
                        shift = 7;
                        *dp++ = (png_byte)d;
                        d = 0;
                    }
                    else
                        shift--;

                }
                if (shift != 7)
                    *dp = (png_byte)d;
                break;
            }
            case 2:
            {
                png_bytep sp;
                png_bytep dp;
                int shift;
                int d;
                int value;
                png_uint_32 i;
                png_uint_32 row_width = row_info->width;

                dp = row;
                shift = 6;
                d = 0;
                for (i = png_pass_start[pass]; i < row_width;
                     i += png_pass_inc[pass])
                {
                    sp = row + (png_size_t)(i >> 2);
                    value = (*sp >> ((3 - (int)(i & 0x03)) << 1)) & 0x03;
                    d |= (value << shift);

                    if (shift == 0)
                    {
                        shift = 6;
                        *dp++ = (png_byte)d;
                        d = 0;
                    }
                    else
                        shift -= 2;
                }
                if (shift != 6)
                    *dp = (png_byte)d;
                break;
            }
            case 4:
            {
                png_bytep sp;
                png_bytep dp;
                int shift;
                int d;
                int value;
                png_uint_32 i;
                png_uint_32 row_width = row_info->width;

                dp = row;
                shift = 4;
                d = 0;
                for (i = png_pass_start[pass]; i < row_width;
                     i += png_pass_inc[pass])
                {
                    sp = row + (png_size_t)(i >> 1);
                    value = (*sp >> ((1 - (int)(i & 0x01)) << 2)) & 0x0f;
                    d |= (value << shift);

                    if (shift == 0)
                    {
                        shift = 4;
                        *dp++ = (png_byte)d;
                        d = 0;
                    }
                    else
                        shift -= 4;
                }
                if (shift != 4)
                    *dp = (png_byte)d;
                break;
            }
            default:
            {
                png_bytep sp;
                png_bytep dp;
                png_uint_32 i;
                png_uint_32 row_width = row_info->width;
                png_size_t pixel_bytes;

                /* Start at the beginning */
                dp = row;
                /* Find out how many bytes each pixel takes up */
                pixel_bytes = (row_info->pixel_depth >> 3);
                /* Loop through the row, only looking at the pixels that
                   matter */
                for (i = png_pass_start[pass]; i < row_width;
                     i += png_pass_inc[pass])
                {
                    /* Find out where the original pixel is */
                    sp = row + (png_size_t)i * pixel_bytes;
                    /* Move the pixel */
                    if (dp != sp)
                        png_memcpy(dp, sp, pixel_bytes);
                    /* Next pixel */
                    dp += pixel_bytes;
                }
                break;
            }
        }
        /* Set new row width */
        row_info->width = (row_info->width +
                           png_pass_inc[pass] - 1 -
                           png_pass_start[pass]) /
                          png_pass_inc[pass];
        row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth,
                                          row_info->width);
    }
}
    #endif

/* This filters the row, chooses which filter to use, if it has not already
 * been specified by the application, and then writes the row out with the
 * chosen filter.
 */
    #define PNG_MAXSUM (((png_uint_32)(-1)) >> 1)
    #define PNG_HISHIFT 10
    #define PNG_LOMASK ((png_uint_32)0xffffL)
    #define PNG_HIMASK ((png_uint_32)(~PNG_LOMASK >> PNG_HISHIFT))
void /* PRIVATE */
png_write_find_filter(png_structp png_ptr, png_row_infop row_info)
{
    png_bytep best_row;
    #ifdef PNG_WRITE_FILTER_SUPPORTED
    png_bytep prev_row, row_buf;
    png_uint_32 mins, bpp;
    png_byte filter_to_do = png_ptr->do_filter;
    png_uint_32 row_bytes = row_info->rowbytes;
    #ifdef PNG_WRITE_WEIGHTED_FILTER_SUPPORTED
    int num_p_filters = (int)png_ptr->num_prev_filters;
    #endif

    png_debug(1, "in png_write_find_filter");

    #ifndef PNG_WRITE_WEIGHTED_FILTER_SUPPORTED
    if (png_ptr->row_number == 0 && filter_to_do == PNG_ALL_FILTERS)
    {
        /* These will never be selected so we need not test them. */
        filter_to_do &= ~(PNG_FILTER_UP | PNG_FILTER_PAETH);
    }
    #endif

    /* Find out how many bytes offset each pixel is */
    bpp = (row_info->pixel_depth + 7) >> 3;

    prev_row = png_ptr->prev_row;
    #endif
    best_row = png_ptr->row_buf;
    #ifdef PNG_WRITE_FILTER_SUPPORTED
    row_buf = best_row;
    mins = PNG_MAXSUM;

    /* The prediction method we use is to find which method provides the
     * smallest value when summing the absolute values of the distances
     * from zero, using anything >= 128 as negative numbers.  This is known
     * as the "minimum sum of absolute differences" heuristic.  Other
     * heuristics are the "weighted minimum sum of absolute differences"
     * (experimental and can in theory improve compression), and the "zlib
     * predictive" method (not implemented yet), which does test compressions
     * of lines using different filter methods, and then chooses the
     * (series of) filter(s) that give minimum compressed data size (VERY
     * computationally expensive).
     *
     * GRR 980525:  consider also
     *   (1) minimum sum of absolute differences from running average (i.e.,
     *       keep running sum of non-absolute differences & count of bytes)
     *       [track dispersion, too?  restart average if dispersion too large?]
     *  (1b) minimum sum of absolute differences from sliding average, probably
     *       with window size <= deflate window (usually 32K)
     *   (2) minimum sum of squared differences from zero or running average
     *       (i.e., ~ root-mean-square approach)
     */


    /* We don't need to test the 'no filter' case if this is the only filter
     * that has been chosen, as it doesn't actually do anything to the data.
     */
    if ((filter_to_do & PNG_FILTER_NONE) &&
        filter_to_do != PNG_FILTER_NONE)
    {
        png_bytep rp;
        png_uint_32 sum = 0;
        png_uint_32 i;
        int v;

        for (i = 0, rp = row_buf + 1; i < row_bytes; i++, rp++)
        {
            v = *rp;
            sum += (v < 128) ? v : 256 - v;
        }

        #ifdef PNG_WRITE_WEIGHTED_FILTER_SUPPORTED
        if (png_ptr->heuristic_method == PNG_FILTER_HEURISTIC_WEIGHTED)
        {
            png_uint_32 sumhi, sumlo;
            int j;
            sumlo = sum & PNG_LOMASK;
            sumhi = (sum >> PNG_HISHIFT) & PNG_HIMASK; /* Gives us some footroom */

            /* Reduce the sum if we match any of the previous rows */
            for (j = 0; j < num_p_filters; j++)
            {
                if (png_ptr->prev_filters[j] == PNG_FILTER_VALUE_NONE)
                {
                    sumlo = (sumlo * png_ptr->filter_weights[j]) >>
                            PNG_WEIGHT_SHIFT;
                    sumhi = (sumhi * png_ptr->filter_weights[j]) >>
                            PNG_WEIGHT_SHIFT;
                }
            }

            /* Factor in the cost of this filter (this is here for completeness,
             * but it makes no sense to have a "cost" for the NONE filter, as
             * it has the minimum possible computational cost - none).
             */
            sumlo = (sumlo * png_ptr->filter_costs[PNG_FILTER_VALUE_NONE]) >>
                    PNG_COST_SHIFT;
            sumhi = (sumhi * png_ptr->filter_costs[PNG_FILTER_VALUE_NONE]) >>
                    PNG_COST_SHIFT;

            if (sumhi > PNG_HIMASK)
                sum = PNG_MAXSUM;
            else
                sum = (sumhi << PNG_HISHIFT) + sumlo;
        }
        #endif
        mins = sum;
    }

    /* Sub filter */
    if (filter_to_do == PNG_FILTER_SUB)
    /* It's the only filter so no testing is needed */
    {
        png_bytep rp, lp, dp;
        png_uint_32 i;
        for (i = 0, rp = row_buf + 1, dp = png_ptr->sub_row + 1; i < bpp;
             i++, rp++, dp++)
        {
            *dp = *rp;
        }
        for (lp = row_buf + 1; i < row_bytes;
             i++, rp++, lp++, dp++)
        {
            *dp = (png_byte)(((int)*rp - (int)*lp) & 0xff);
        }
        best_row = png_ptr->sub_row;
    }

    else if (filter_to_do & PNG_FILTER_SUB)
    {
        png_bytep rp, dp, lp;
        png_uint_32 sum = 0, lmins = mins;
        png_uint_32 i;
        int v;

        #ifdef PNG_WRITE_WEIGHTED_FILTER_SUPPORTED
        /* We temporarily increase the "minimum sum" by the factor we
         * would reduce the sum of this filter, so that we can do the
         * early exit comparison without scaling the sum each time.
         */
        if (png_ptr->heuristic_method == PNG_FILTER_HEURISTIC_WEIGHTED)
        {
            int j;
            png_uint_32 lmhi, lmlo;
            lmlo = lmins & PNG_LOMASK;
            lmhi = (lmins >> PNG_HISHIFT) & PNG_HIMASK;

            for (j = 0; j < num_p_filters; j++)
            {
                if (png_ptr->prev_filters[j] == PNG_FILTER_VALUE_SUB)
                {
                    lmlo = (lmlo * png_ptr->inv_filter_weights[j]) >>
                           PNG_WEIGHT_SHIFT;
                    lmhi = (lmhi * png_ptr->inv_filter_weights[j]) >>
                           PNG_WEIGHT_SHIFT;
                }
            }

            lmlo = (lmlo * png_ptr->inv_filter_costs[PNG_FILTER_VALUE_SUB]) >>
                   PNG_COST_SHIFT;
            lmhi = (lmhi * png_ptr->inv_filter_costs[PNG_FILTER_VALUE_SUB]) >>
                   PNG_COST_SHIFT;

            if (lmhi > PNG_HIMASK)
                lmins = PNG_MAXSUM;
            else
                lmins = (lmhi << PNG_HISHIFT) + lmlo;
        }
        #endif

        for (i = 0, rp = row_buf + 1, dp = png_ptr->sub_row + 1; i < bpp;
             i++, rp++, dp++)
        {
            v = *dp = *rp;

            sum += (v < 128) ? v : 256 - v;
        }
        for (lp = row_buf + 1; i < row_bytes;
             i++, rp++, lp++, dp++)
        {
            v = *dp = (png_byte)(((int)*rp - (int)*lp) & 0xff);

            sum += (v < 128) ? v : 256 - v;

            if (sum > lmins) /* We are already worse, don't continue. */
                break;
        }

        #ifdef PNG_WRITE_WEIGHTED_FILTER_SUPPORTED
        if (png_ptr->heuristic_method == PNG_FILTER_HEURISTIC_WEIGHTED)
        {
            int j;
            png_uint_32 sumhi, sumlo;
            sumlo = sum & PNG_LOMASK;
            sumhi = (sum >> PNG_HISHIFT) & PNG_HIMASK;

            for (j = 0; j < num_p_filters; j++)
            {
                if (png_ptr->prev_filters[j] == PNG_FILTER_VALUE_SUB)
                {
                    sumlo = (sumlo * png_ptr->inv_filter_weights[j]) >>
                            PNG_WEIGHT_SHIFT;
                    sumhi = (sumhi * png_ptr->inv_filter_weights[j]) >>
                            PNG_WEIGHT_SHIFT;
                }
            }

            sumlo = (sumlo * png_ptr->inv_filter_costs[PNG_FILTER_VALUE_SUB]) >>
                    PNG_COST_SHIFT;
            sumhi = (sumhi * png_ptr->inv_filter_costs[PNG_FILTER_VALUE_SUB]) >>
                    PNG_COST_SHIFT;

            if (sumhi > PNG_HIMASK)
                sum = PNG_MAXSUM;
            else
                sum = (sumhi << PNG_HISHIFT) + sumlo;
        }
        #endif

        if (sum < mins)
        {
            mins = sum;
            best_row = png_ptr->sub_row;
        }
    }

    /* Up filter */
    if (filter_to_do == PNG_FILTER_UP)
    {
        png_bytep rp, dp, pp;
        png_uint_32 i;

        for (i = 0, rp = row_buf + 1, dp = png_ptr->up_row + 1,
             pp = prev_row + 1; i < row_bytes;
             i++, rp++, pp++, dp++)
        {
            *dp = (png_byte)(((int)*rp - (int)*pp) & 0xff);
        }
        best_row = png_ptr->up_row;
    }

    else if (filter_to_do & PNG_FILTER_UP)
    {
        png_bytep rp, dp, pp;
        png_uint_32 sum = 0, lmins = mins;
        png_uint_32 i;
        int v;


        #ifdef PNG_WRITE_WEIGHTED_FILTER_SUPPORTED
        if (png_ptr->heuristic_method == PNG_FILTER_HEURISTIC_WEIGHTED)
        {
            int j;
            png_uint_32 lmhi, lmlo;
            lmlo = lmins & PNG_LOMASK;
            lmhi = (lmins >> PNG_HISHIFT) & PNG_HIMASK;

            for (j = 0; j < num_p_filters; j++)
            {
                if (png_ptr->prev_filters[j] == PNG_FILTER_VALUE_UP)
                {
                    lmlo = (lmlo * png_ptr->inv_filter_weights[j]) >>
                           PNG_WEIGHT_SHIFT;
                    lmhi = (lmhi * png_ptr->inv_filter_weights[j]) >>
                           PNG_WEIGHT_SHIFT;
                }
            }

            lmlo = (lmlo * png_ptr->inv_filter_costs[PNG_FILTER_VALUE_UP]) >>
                   PNG_COST_SHIFT;
            lmhi = (lmhi * png_ptr->inv_filter_costs[PNG_FILTER_VALUE_UP]) >>
                   PNG_COST_SHIFT;

            if (lmhi > PNG_HIMASK)
                lmins = PNG_MAXSUM;
            else
                lmins = (lmhi << PNG_HISHIFT) + lmlo;
        }
        #endif

        for (i = 0, rp = row_buf + 1, dp = png_ptr->up_row + 1,
             pp = prev_row + 1; i < row_bytes; i++)
        {
            v = *dp++ = (png_byte)(((int)*rp++ - (int)*pp++) & 0xff);

            sum += (v < 128) ? v : 256 - v;

            if (sum > lmins) /* We are already worse, don't continue. */
                break;
        }

        #ifdef PNG_WRITE_WEIGHTED_FILTER_SUPPORTED
        if (png_ptr->heuristic_method == PNG_FILTER_HEURISTIC_WEIGHTED)
        {
            int j;
            png_uint_32 sumhi, sumlo;
            sumlo = sum & PNG_LOMASK;
            sumhi = (sum >> PNG_HISHIFT) & PNG_HIMASK;

            for (j = 0; j < num_p_filters; j++)
            {
                if (png_ptr->prev_filters[j] == PNG_FILTER_VALUE_UP)
                {
                    sumlo = (sumlo * png_ptr->filter_weights[j]) >>
                            PNG_WEIGHT_SHIFT;
                    sumhi = (sumhi * png_ptr->filter_weights[j]) >>
                            PNG_WEIGHT_SHIFT;
                }
            }

            sumlo = (sumlo * png_ptr->filter_costs[PNG_FILTER_VALUE_UP]) >>
                    PNG_COST_SHIFT;
            sumhi = (sumhi * png_ptr->filter_costs[PNG_FILTER_VALUE_UP]) >>
                    PNG_COST_SHIFT;

            if (sumhi > PNG_HIMASK)
                sum = PNG_MAXSUM;
            else
                sum = (sumhi << PNG_HISHIFT) + sumlo;
        }
        #endif

        if (sum < mins)
        {
            mins = sum;
            best_row = png_ptr->up_row;
        }
    }

    /* Avg filter */
    if (filter_to_do == PNG_FILTER_AVG)
    {
        png_bytep rp, dp, pp, lp;
        png_uint_32 i;
        for (i = 0, rp = row_buf + 1, dp = png_ptr->avg_row + 1,
             pp = prev_row + 1; i < bpp; i++)
        {
            *dp++ = (png_byte)(((int)*rp++ - ((int)*pp++ / 2)) & 0xff);
        }
        for (lp = row_buf + 1; i < row_bytes; i++)
        {
            *dp++ = (png_byte)(((int)*rp++ - (((int)*pp++ + (int)*lp++) / 2))
                               & 0xff);
        }
        best_row = png_ptr->avg_row;
    }

    else if (filter_to_do & PNG_FILTER_AVG)
    {
        png_bytep rp, dp, pp, lp;
        png_uint_32 sum = 0, lmins = mins;
        png_uint_32 i;
        int v;

        #ifdef PNG_WRITE_WEIGHTED_FILTER_SUPPORTED
        if (png_ptr->heuristic_method == PNG_FILTER_HEURISTIC_WEIGHTED)
        {
            int j;
            png_uint_32 lmhi, lmlo;
            lmlo = lmins & PNG_LOMASK;
            lmhi = (lmins >> PNG_HISHIFT) & PNG_HIMASK;

            for (j = 0; j < num_p_filters; j++)
            {
                if (png_ptr->prev_filters[j] == PNG_FILTER_VALUE_AVG)
                {
                    lmlo = (lmlo * png_ptr->inv_filter_weights[j]) >>
                           PNG_WEIGHT_SHIFT;
                    lmhi = (lmhi * png_ptr->inv_filter_weights[j]) >>
                           PNG_WEIGHT_SHIFT;
                }
            }

            lmlo = (lmlo * png_ptr->inv_filter_costs[PNG_FILTER_VALUE_AVG]) >>
                   PNG_COST_SHIFT;
            lmhi = (lmhi * png_ptr->inv_filter_costs[PNG_FILTER_VALUE_AVG]) >>
                   PNG_COST_SHIFT;

            if (lmhi > PNG_HIMASK)
                lmins = PNG_MAXSUM;
            else
                lmins = (lmhi << PNG_HISHIFT) + lmlo;
        }
        #endif

        for (i = 0, rp = row_buf + 1, dp = png_ptr->avg_row + 1,
             pp = prev_row + 1; i < bpp; i++)
        {
            v = *dp++ = (png_byte)(((int)*rp++ - ((int)*pp++ / 2)) & 0xff);

            sum += (v < 128) ? v : 256 - v;
        }
        for (lp = row_buf + 1; i < row_bytes; i++)
        {
            v = *dp++ =
                    (png_byte)(((int)*rp++ - (((int)*pp++ + (int)*lp++) / 2)) & 0xff);

            sum += (v < 128) ? v : 256 - v;

            if (sum > lmins) /* We are already worse, don't continue. */
                break;
        }

        #ifdef PNG_WRITE_WEIGHTED_FILTER_SUPPORTED
        if (png_ptr->heuristic_method == PNG_FILTER_HEURISTIC_WEIGHTED)
        {
            int j;
            png_uint_32 sumhi, sumlo;
            sumlo = sum & PNG_LOMASK;
            sumhi = (sum >> PNG_HISHIFT) & PNG_HIMASK;

            for (j = 0; j < num_p_filters; j++)
            {
                if (png_ptr->prev_filters[j] == PNG_FILTER_VALUE_NONE)
                {
                    sumlo = (sumlo * png_ptr->filter_weights[j]) >>
                            PNG_WEIGHT_SHIFT;
                    sumhi = (sumhi * png_ptr->filter_weights[j]) >>
                            PNG_WEIGHT_SHIFT;
                }
            }

            sumlo = (sumlo * png_ptr->filter_costs[PNG_FILTER_VALUE_AVG]) >>
                    PNG_COST_SHIFT;
            sumhi = (sumhi * png_ptr->filter_costs[PNG_FILTER_VALUE_AVG]) >>
                    PNG_COST_SHIFT;

            if (sumhi > PNG_HIMASK)
                sum = PNG_MAXSUM;
            else
                sum = (sumhi << PNG_HISHIFT) + sumlo;
        }
        #endif

        if (sum < mins)
        {
            mins = sum;
            best_row = png_ptr->avg_row;
        }
    }

    /* Paeth filter */
    if (filter_to_do == PNG_FILTER_PAETH)
    {
        png_bytep rp, dp, pp, cp, lp;
        png_uint_32 i;
        for (i = 0, rp = row_buf + 1, dp = png_ptr->paeth_row + 1,
             pp = prev_row + 1; i < bpp; i++)
        {
            *dp++ = (png_byte)(((int)*rp++ - (int)*pp++) & 0xff);
        }

        for (lp = row_buf + 1, cp = prev_row + 1; i < row_bytes; i++)
        {
            int a, b, c, pa, pb, pc, p;

            b = *pp++;
            c = *cp++;
            a = *lp++;

            p = b - c;
            pc = a - c;

            #ifdef PNG_USE_ABS
            pa = abs(p);
            pb = abs(pc);
            pc = abs(p + pc);
            #else
            pa = p < 0 ? -p : p;
            pb = pc < 0 ? -pc : pc;
            pc = (p + pc) < 0 ? -(p + pc) : p + pc;
            #endif

            p = (pa <= pb && pa <= pc) ? a : (pb <= pc) ? b : c;

            *dp++ = (png_byte)(((int)*rp++ - p) & 0xff);
        }
        best_row = png_ptr->paeth_row;
    }

    else if (filter_to_do & PNG_FILTER_PAETH)
    {
        png_bytep rp, dp, pp, cp, lp;
        png_uint_32 sum = 0, lmins = mins;
        png_uint_32 i;
        int v;

        #ifdef PNG_WRITE_WEIGHTED_FILTER_SUPPORTED
        if (png_ptr->heuristic_method == PNG_FILTER_HEURISTIC_WEIGHTED)
        {
            int j;
            png_uint_32 lmhi, lmlo;
            lmlo = lmins & PNG_LOMASK;
            lmhi = (lmins >> PNG_HISHIFT) & PNG_HIMASK;

            for (j = 0; j < num_p_filters; j++)
            {
                if (png_ptr->prev_filters[j] == PNG_FILTER_VALUE_PAETH)
                {
                    lmlo = (lmlo * png_ptr->inv_filter_weights[j]) >>
                           PNG_WEIGHT_SHIFT;
                    lmhi = (lmhi * png_ptr->inv_filter_weights[j]) >>
                           PNG_WEIGHT_SHIFT;
                }
            }

            lmlo = (lmlo * png_ptr->inv_filter_costs[PNG_FILTER_VALUE_PAETH]) >>
                   PNG_COST_SHIFT;
            lmhi = (lmhi * png_ptr->inv_filter_costs[PNG_FILTER_VALUE_PAETH]) >>
                   PNG_COST_SHIFT;

            if (lmhi > PNG_HIMASK)
                lmins = PNG_MAXSUM;
            else
                lmins = (lmhi << PNG_HISHIFT) + lmlo;
        }
        #endif

        for (i = 0, rp = row_buf + 1, dp = png_ptr->paeth_row + 1,
             pp = prev_row + 1; i < bpp; i++)
        {
            v = *dp++ = (png_byte)(((int)*rp++ - (int)*pp++) & 0xff);

            sum += (v < 128) ? v : 256 - v;
        }

        for (lp = row_buf + 1, cp = prev_row + 1; i < row_bytes; i++)
        {
            int a, b, c, pa, pb, pc, p;

            b = *pp++;
            c = *cp++;
            a = *lp++;

            #ifndef PNG_SLOW_PAETH
            p = b - c;
            pc = a - c;
            #ifdef PNG_USE_ABS
            pa = abs(p);
            pb = abs(pc);
            pc = abs(p + pc);
            #else
            pa = p < 0 ? -p : p;
            pb = pc < 0 ? -pc : pc;
            pc = (p + pc) < 0 ? -(p + pc) : p + pc;
            #endif
            p = (pa <= pb && pa <= pc) ? a : (pb <= pc) ? b : c;
            #else /* PNG_SLOW_PAETH */
            p = a + b - c;
            pa = abs(p - a);
            pb = abs(p - b);
            pc = abs(p - c);
            if (pa <= pb && pa <= pc)
                p = a;
            else if (pb <= pc)
                p = b;
            else
                p = c;
            #endif /* PNG_SLOW_PAETH */

            v = *dp++ = (png_byte)(((int)*rp++ - p) & 0xff);

            sum += (v < 128) ? v : 256 - v;

            if (sum > lmins) /* We are already worse, don't continue. */
                break;
        }

        #ifdef PNG_WRITE_WEIGHTED_FILTER_SUPPORTED
        if (png_ptr->heuristic_method == PNG_FILTER_HEURISTIC_WEIGHTED)
        {
            int j;
            png_uint_32 sumhi, sumlo;
            sumlo = sum & PNG_LOMASK;
            sumhi = (sum >> PNG_HISHIFT) & PNG_HIMASK;

            for (j = 0; j < num_p_filters; j++)
            {
                if (png_ptr->prev_filters[j] == PNG_FILTER_VALUE_PAETH)
                {
                    sumlo = (sumlo * png_ptr->filter_weights[j]) >>
                            PNG_WEIGHT_SHIFT;
                    sumhi = (sumhi * png_ptr->filter_weights[j]) >>
                            PNG_WEIGHT_SHIFT;
                }
            }

            sumlo = (sumlo * png_ptr->filter_costs[PNG_FILTER_VALUE_PAETH]) >>
                    PNG_COST_SHIFT;
            sumhi = (sumhi * png_ptr->filter_costs[PNG_FILTER_VALUE_PAETH]) >>
                    PNG_COST_SHIFT;

            if (sumhi > PNG_HIMASK)
                sum = PNG_MAXSUM;
            else
                sum = (sumhi << PNG_HISHIFT) + sumlo;
        }
        #endif

        if (sum < mins)
        {
            best_row = png_ptr->paeth_row;
        }
    }
    #endif /* PNG_WRITE_FILTER_SUPPORTED */
    /* Do the actual writing of the filtered row data from the chosen filter. */

    png_write_filtered_row(png_ptr, best_row);

    #ifdef PNG_WRITE_FILTER_SUPPORTED
    #ifdef PNG_WRITE_WEIGHTED_FILTER_SUPPORTED
    /* Save the type of filter we picked this time for future calculations */
    if (png_ptr->num_prev_filters > 0)
    {
        int j;
        for (j = 1; j < num_p_filters; j++)
        {
            png_ptr->prev_filters[j] = png_ptr->prev_filters[j - 1];
        }
        png_ptr->prev_filters[j] = best_row[0];
    }
    #endif
    #endif /* PNG_WRITE_FILTER_SUPPORTED */
}


/* Do the actual writing of a previously filtered row. */
void /* PRIVATE */
png_write_filtered_row(png_structp png_ptr, png_bytep filtered_row)
{
    png_debug(1, "in png_write_filtered_row");

    png_debug1(2, "filter = %d", filtered_row[0]);
    /* Set up the zlib input buffer */

    png_ptr->zstream.next_in = filtered_row;
    png_ptr->zstream.avail_in = (uInt)png_ptr->row_info.rowbytes + 1;
    /* Repeat until we have compressed all the data */
    do
    {
        int ret; /* Return of zlib */

        /* Compress the data */
        ret = deflate(&png_ptr->zstream, Z_NO_FLUSH);
        /* Check for compression errors */
        if (ret != Z_OK)
        {
            if (png_ptr->zstream.msg != NULL)
                png_error(png_ptr, png_ptr->zstream.msg);
            else
                png_error(png_ptr, "zlib error");
        }

        /* See if it is time to write another IDAT */
        if (!(png_ptr->zstream.avail_out))
        {
            /* Write the IDAT and reset the zlib output buffer */
            png_write_IDAT(png_ptr, png_ptr->zbuf, png_ptr->zbuf_size);
            png_ptr->zstream.next_out = png_ptr->zbuf;
            png_ptr->zstream.avail_out = (uInt)png_ptr->zbuf_size;
        }
        /* Repeat until all data has been compressed */
    }
    while (png_ptr->zstream.avail_in);

    /* Swap the current and previous rows */
    if (png_ptr->prev_row != NULL)
    {
        png_bytep tptr;

        tptr = png_ptr->prev_row;
        png_ptr->prev_row = png_ptr->row_buf;
        png_ptr->row_buf = tptr;
    }

    /* Finish row - updates counters and flushes zlib if last row */
    png_write_finish_row(png_ptr);

    #ifdef PNG_WRITE_FLUSH_SUPPORTED
    png_ptr->flush_rows++;

    if (png_ptr->flush_dist > 0 &&
        png_ptr->flush_rows >= png_ptr->flush_dist)
    {
        png_write_flush(png_ptr);
    }
    #endif
}
#endif /* PNG_WRITE_SUPPORTED */